1. Field of the Invention
The present invention relates to a motor control system and a motor control method and, more particularly a motor control system and a motor control method using a resolver.
2. Description of Related Art
In an electric vehicle, particularly in a hybrid type electric vehicle, a more efficient drive system is required in order to improve the driving range. Therefore, a synchronous machine such as a synchronous motor or a synchronous generator using permanent magnets come to be widely used instead of a heavy-duty induction motor.
In order to control the motor of these kind, a rotary sensor for detecting a pole position is necessary. The rotary sensors can be roughly classified into an optical type and a resolver type. As an example of the resolver type rotary sensor, Japanese Patent Application Laid-Open No.9-72758 discloses a winding break detecting system including a resolver and an R/D converter and a method of detecting a winding break.
On the other hand, in the hybrid type electric vehicle, a motor and a transmission mechanism of an engine are required to be made small in size and light in weight by integrating them in a unit.
In this case, although the rotary sensor for detecting the magnetic pole position of the motor is also arranged at a position near the engine together with the transmission mechanism, the position is not a desirable environment for the rotary sensor because it is an oil mist producing environment. Therefore, in the electric vehicle employing a hybrid system as the driving method, the resolver type rotary sensor is more suitable than the optical type rotary sensor.
Inventions of using a resolver as a rotary sensor are disclosed in Japanese Patent Application Laid-Open No.5-322598 and Japanese Patent Application Laid-Open No.61-210889. The invention of Japanese Patent Application Laid-Open No.5-322598 is that an R/D converter is operated in synchronism with position control calculation. The invention of Japanese Patent Application Laid-Open No. 61-210889 is that in a resolver of 2-phase exciting 1-phase output type, a PWM signal is generated in synchronism with the output signal.
In the conventional resolver type rotary sensor, a phase error sometimes occurs because the rotary sensor is affected by the switching noise due to the PWM signal of the inverter when current of the motor is changed.
When a phase error occurs in an output of the R/D converter due to the noise, disturbance occurs in the winding current of the motor. This disturbance in the winding current causes occurrence of noise and deterioration of the control characteristic of the electric vehicle.
On the other hand, in the invention of Japanese Patent Application Laid-Open No.61-210889, an angle of rotating xcex8 is detected from a phase difference between an exciting signal and an output signal in a 2-phase exciting 1-phase output type resolver. Further, The PWM signal is generated completely in synchronism with the cycle of the detected signal. The inverter generates switching noise at an ON-OFF timing of the PWM signal, that is, at a switching timing of the power element. Since the phase detecting timing, that is, the zero-cross point of the output signal, therefore, always agree with the ON-OFF timing of the PWM signal, the detected signal is apt to be affected by the switching noise.
An object of the present invention is to provide a motor control system comprising an R/D converter which is capable of outputting a good phase signal without being affected by the switching noise due to a PWM signal of an inverter and a motor control method.
This and other objects and advantages are achieved by the motor control system according to the invention in which a motor having a resolver as a rotary sensor is driven by an inverter, which in turn is controlled by a control unit. The control unit executes phase calculation processing, based on a phase signal that is output from the resolver and converted by an R/D converter. A voltage reference is calculated based on current reference and a current value of the motor; and a PWM signal is generated for controlling the inverter based on the voltage reference. The control unit generates a PWM synchronism signal in synchronism with the PWM signal, and the R/D converter is driven using the PWM synchronism signal.
Another feature of the present invention is that the exciting signal of the R/D converter and a starting signal of the A/D converter for acquiring the detected signal of the resolver are synchronized with the PWM synchronism signal.
According to still another feature of the invention, the PWM synchronism signal is synchronized with a timing of a maximum value of or minimum value of a PWM carrier signal.
According to a still further feature of the invention the R/D converter of the control unit includes an exciting signal generating unit for supplying current to an exciting winding of the resolver, and an A/D converter which converts analogue output of a sin-winding and a cos-winding into digital signals. A xcex8 calculation processing unit calculates tan xcex8 and cot xcex8 by a division process, based on the converted digital signal, and calculates a phase angle xcex80 to a rotating angle xcex8 of the resolver from the tan xcex8 and cot xcex8 through a function table. The division process calculates tan xcex8 and cot xcex8 using a transfer function 1/(S+KA cos xcex8) or 1/(S+KA sin xcex8) which uses multiplication processing.
According to the present invention, it is possible to provide a motor control system comprising an R/D converter which is capable of outputting a good phase signal without being affected by the switching noise due to a PWM signal of an inverter and a motor control method.